This invention relates generally to soil stabilization, and more particularly to the prefabricated vertical earth drains used to accelerate consolidation of soft clays.
The present invention pertains to improvements in prefabricated vertical earth drains of the type disclosed in the present inventor's U.S. Pat. No. 5,820,296. Reference should be made to the discussion presented in the background of the disclosure of this patent for an understanding of the uses and applications of such prefabricated vertical earth drains.
Prior art prefabricated vertical earth drains are usually either configured of elongated corrugated strips of flexible plastic core sheets having horizontal corrugations which provide continuous longitudinally extending drains in the vertical direction, which longitudinal corrugations are defined with sharp corner bends, as disclosed in the inventor's previously mentioned U.S. Pat. No. 5,820,296; or they are constructed with flexible plastic core sheets which have a dimpled or studded surface configuration as illustrated in U.S. Pat. Nos. 4,749,306; 4,943,185 and 5,489,462, or as illustrated in FIGS. 1 and 2 of the drawings attached to this specification. In FIGS. 1 and 2 the core sheet 10 is diagrammatically and schematically shown and provided with multiple uniformly spaced studs 11 of solid cross section. These prefabricated vertical earth drains are composite in construction in that the plastic core or cores are provided with an outer wrap or surrounding of filter fabric 12 generally referred to as geofabric or geotextile in the industry which prevents clogging of the water drains provided in the core material with particles of soil or earth.
While the prefabricated composite vertical earth drains as described in the inventor's U.S. Pat. No. 5,820,296 do provide considerable improvement over the prior art in that added strength is provided to the core material by the added reliefs to assist in preventing collapsing of the cores from soil pressure whereby buckling or folding of the core is experienced, nevertheless, room for improvement remains. In addition, another problem also exists with the composite prefabricated earth drains of the type disclosed in the inventors previously referenced patent and in the other prior art types previously referenced in that under compressive forces applied when the drain is imbedded in the earth, the geofabric or filter fabric is compressively deformed excessively depressed into recesses of these core drain channels and the drain channels themselves are deformed and made more shallow. Accordingly, the added sag or protrusion of the geofabric into the drain channels of the core and deformation of the drain channels constricts the flow of water thereby reducing the efficiency and flow capacity of the drain.
This latter mentioned problem is illustrated in FIGS. 1 and 2 which illustrate the geofabric sag pattern over the studded drain core 10 (FIG. 1 in perspective and FIG. 2 in cross section) and deformed under pressure as would occur when the drain is imbedded in the earth.
In this regard, note that the geofabric 12 fully surrounds the flexible drain core sheet 10 which is provided with multiple dimples or studs 11. The geofabric 12 sags between the studs to an undesirably low level as indicated at 13 and further fully engages and depresses the geofabric 12 against the outer surfaces of the studs 11 as indicated at 14 thereby considerably constricting the flow of water between, over and around the studs.
Similarly, with reference to FIG. 3, a cross section of the composite drain members of the type illustrated in the inventor's U.S. Pat. No. 5,820,296 is illustrated with the geofabric and core drain channels being deformed under pressure as indicated by arrows 15 applied by the surrounding earth. Here the corrugated drain member core 16 is provided with vertical drain channels 17 and relief protrusions 18.
In this illustration, the channels 17 do remain in a more open condition than the channels provided between solid studs 14 of the core structure shown in FIG. 2, however, the core structure deforms and the geofabric 12 compresses against the outer sides of the channels against the relief protrusions 18 thereby limiting the water flow capabilities of and between the respective channels 17 excessively as illustrated. In addition, this corrugated core material of sharp angled corrugation bends, while strengthened by the relief protrusions 18 to lessen the possibility of deforming and folding in the core member 16 in the horizontal direction indicated by arrow 22, nevertheless is still prone to possible horizontal folding, although not to the excessive extent encountered with the other prior art corrugated or dimpled core members or sheets.